Optical disk media are capable of storing a considerable amount of data in the form of small marks or holes in the surface of the disk, each representing a bit of data. The marks, burned into the surface of the disk by a laser, are arranged along spiral tracks, each divided into a number of sectors.
FIG. 5 is a diagram of an apparatus 10 for reading data prerecorded on an optical disk 12. The disk 12 is rotated by a disk servo 14 comprising a precisely controllable DC motor. A laser 16 irradiates the surface of the disk 12, and light reflected from the disk impinges on the surface of a detector 18. An optical head 20, located between the disk 12 and laser-detector 16, 18 is positioned by another servo (not shown) to read data from a desired track. Writing is carried out using similar optics, with the optical medium being preheated to enable light from laser 16 to form surface marks corresponding to data. The servos and laser/detector are controlled by a microprocessor 22.
The components comprising apparatus 10 shown in FIG. 5 typically are arranged with a common housing, such as provided by SCSI (Small Computer System Interface) resident at a personal computer or other computer requiring storage of a large quantity of data. The data storage capacity of the disk 12 is enhanced in some systems by utilizing both sides of a disk such as a 130 mm (51/4 inch) optical disk.
Data read and write logic, implemented by microprocessor 22 in the representative illustration of FIG. 5, has been carried out by commercially available special function integrated circuits, such as the AM95C96 optical disk controller (ODC), manufactured by Advanced Micro Devices of Sunnyvale, Calif. A system implementing the AM95C96, shown in FIG. 1, comprises ODC 24 reading data through an encoder/decoder (ODE) 28 and a phase locked loop (PLL) 30 off the optical disk and writing to the optical disk. A CPU 32 controls seeking to the desired location on the disk. The ODC/ODE 24, 28 interfaces with CPU 32, working memory 34 and a disk interface 36 to process the applied data signals and transfer commands for compliance with particular specifications such as the X3B11 continuous composite servo (CCS), WORM/ERASABLE optical format developed by ANSI.
The ODC 24 is interfaced to a system bus by host interface unit 38, and is supported by buffer memory 40 and error processor 42. General operation of the system shown in FIG. 1, being known to the prior art, is not described in detail. An improvement integrating the ODC/ODE 24, 26 as a single functional element is described in my copending application Ser. No. 07/813,275, filed concurrently herewith.
FIG. 4 depicts the layout of tracks on an optical disk. The tracks are arranged along a spiral path on the surface of the disk 12, with each turn of the spiral being treated as a separate track. In one example, the optical disk may be 90 mm in diameter, and may contain 10,000 tracks (numbered 0-9999 FIG. 7); each track is divided into twenty-five (25) sectors. Each sector in turn will carry 725 bytes of unformatted data. The optical disk in this example is capable of storing 181,250,000 bytes of data, or about 100,000 pates of text. Modifications include implementing more densely packed sectors, larger diameter disks and/or double-sided storage for enhanced information storage capacity.
FIG. 2 is a field diagram of the X3B11 format, comprising a header area that is "pre-stamped", followed by a data area for receiving data for storage. The first field of the header is a sector mark (SM) having a special redundant pattern. This field identifies the start of a sector. The SM field as well as the other fields constituting the X3B11 format is summarized below in Table I.
TABLE I __________________________________________________________________________ NAME FUNCTION PATTERN __________________________________________________________________________ SM Sector Mark 80 channel bits (5 bytes) Special Redundant Pattern = 5 3 3 7 3 3 3 3 5 long burn followed by 0010010010= 1111111111000000111111000000000000001111110000001 111110000001111111111 0010010010 VFO1, 2, 3 Lock up field for PLL Continuous Pattern VFO1 = 01001001001 . . . 010010 VFO2' = 10010010010 . . . 010010 VFOI" = 00010010010 . . . 010010 VFO3 = 01001001001 . . . 010010 Note: VFO2 varies depending on previous pattern in CRC AM Address Mark (Bit/Byte Sync) 0100 1000 0000 0100 16 Channel bits. (1 byte) ID Track No. (2 bytes) High order/Low order Sector No. (1 byte) bits 7-6 = ID Numba (ID 0-2) bit 5 = 0 Reserved bits 4-0 = Sector Number CRC ID Field Check Bytes (2 bytes) CRC Polynominal seed = 1's
Postamble (one byte) Allows last CRC and and Data byte closure under RLL (2,7) modulation ODF Offset Detection Flag (one byte) Not written, no grooves GAP Gap (Splice) Unformatted area FLAG Indicate Written Block Continuous Pulse (5 byte area, decision by majority) 100100100100100100100100100 . . . ALPC Auto Laser Power Control Blank 2 bytes zone SYNC Redundant Sync for Data Triple sync pattern 0100 0010 0100 0010 0010 0010 0100 0100 1000 0010 0100 1000 DATA User Data, Control, CRC, ECC See FIGS. 1.6 and 1.7. and RESYNC bytes. BUFFER Used for RPM timing margins Not Written area RESYNC Data Filed byte sync 0010 0000 0010 0100 16 Channel bits (1 byte) __________________________________________________________________________ NOTE: All bit patterns show channel code bits in RLL (2,7) modulation.
During both reading and writing operations, ODE 26 detects sector mark (SM) once within each sector. Referring to Table I, the sector mark comprises 80 bits arranged as a long burn followed by a transition pattern. Sector mark decoding is carried out by monitoring the long burn pattern of the track, and identifying a pattern characteristic of the sector mark. A particularly robust algorithm that this purpose is described in my copending application Ser. No. 07/810,574, entitled "Sector Mark Detection in Long Burn Pattern for Optical Data Disks," filed concurrently herewith and incorporated by reference.
Detection of the sector mark pattern is a prerequisite to recovery of data from the corresponding sector. It provides synchronization to the region of each sector from which data is to be recovered or is to be written. The data field of each sector resides at a predefined distance, in bytes, from the end of the sector mark pattern. The number of bytes depends on the particular standard involved. For example, in the conventional X3B11 format, shown symbolically in FIG. 2, the pre-stamped, or read only (RO), region extends 47 bytes beyond the sector mark field SM, followed by a magneto-optic region (MO) upon which data can be written once (the MO region is also termed a "WORM", or write once-read many, region). The data region of a 90 mm, 512 byte sector size by convention follows the RO region by ODF and GAP bytes. The next sector mark field follows the data field by a suffer region of 13 bytes for timing margins.
If the sector mark pattern for a sector is not detected because the sector mark pattern is obscured by dirt or is defective for another reason, the data field for that sector cannot be accessed. Prior art optical data disk controllers improve data recovery from optical disks by searching the track of an optical data disk for the presence f sector mark patterns in the appropriate fields, and applying a pseudo sector mark pattern to each sector in which a sector mark pattern is not detected. Upon detection of either a sector mark pattern or generation of a pseudo sector mark, a "sector mark found" signal is issued. In response to this signal, a data recovery routine is initiated to access data from the data field of the current sector. Data recovery from a sector having a defective sector mark field thus is achieved.
However, if the disk has a considerable number of sectors with defective sector marks, the disk itself may be defective, and should not be used. The user should be appraised of the possibly defective quality of a disk before data is written to it.
A feature of the present invention not only recovers from optical data disks having sectors with defective sector marks, but also limits the amount of such data recovered while identifying the user of the presence of an excessive number of sectors with defective sector marks. Another feature inhibits writing to the data field of a sector deemed possibly defective as a result of a defective sector mark field.
Optical data disks are supplied in any of several formats. The format of a new, unmarked disk may have to be ascertained by the user in a procedure termed "certification." However, it is desirable to implement media certification without imposing a requirement for additional equipment. Another feature of this invention, therefore, implements sector mark detection as a mechanism for media certification of an optical data disk.